IIT-JEE 2007 · Paper 1, Chemistry question 23

Bond orders (MO theory). CO has 14 electrons, bond order 3. $\ce{NO+}$, $\ce{CN-}$ and $\ce{N2}$ are isoelectronic with it (14 electrons), so also 3.

$\ce{NO-}$ has 16 electrons: $\frac{10-6}{2}=2$.

(A)